Catalytic carboxylation of alkanes

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Organizational Unit

Publications

Pyrazole and trispyrazolylmethane rhenium complexes as catalysts for ethane and cyclohexane oxidations

Publication . Alegria, Elisabete; Kirillova, Marina V.; Martins, Luisa; Pombeiro, Armando

The pyrazole complexes [ReCl2{N2C(O)Ph}(Hpz)(PPh3)2] 2 (Hpz = pyrazole), [ReCl2{N2C(O)Ph}(Hpz)2(PPh3)] 3 and [ReClF{N2C(O)Ph}(Hpz)2(PPh3)] 4, and the tris(pyrazolyl)methane compounds [ReCl2(HCpz3)(PPh3)][BF4] 5 (pz = pyrazolyl), [ReCl3{HC(pz)3}] 7, [ReOCl2{SO3C(pz)3}(PPh3)] 8 and [ReO3{SO3C(pz)3}] 9, and their precursors [ReCl2{η2-N,O-N2C(O)Ph}(PPh3)2] 1 and [ReOCl3(PPh3)2] 6, act as selective catalysts (or catalyst precursors), in a single-pot process, for the oxidation of ethane, in the presence of potassium peroxodisulfate K2S2O8, in trifluoroacetic acid (TFA), to give acetic acid, in a remarkable yield (up to ca. 40%) and under mild conditions (in some cases carboxylation can also occur to give propionic acid, but in a much lower yield). The catalytic peroxidative oxidation of ethane to acetaldehyde and of cyclohexane to cyclohexanone and cyclohexanol by an aqueous solution of H2O2 at room temperature is also achieved by using most of those catalyst precursors. The effects of a variety of factors were studied towards the optimization of the processes which are shown to proceed via both C-centered and O-centered radical mechanisms.

2007-01-27Journal article

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Rhenium complexes of tris(pyrazolyl)methanes and sulfonate derivative

Publication . Alegria, Elisabete; Martins, Luisa; Haukka, Matti; Pombeiro, Armando

The trioxo [ReO3{SO3C(pz)3}] (1) (pz = pyrazolyl) and oxo [ReOCl{SO3C(pz)3}(PPh3)]Cl (2) compounds with tris(pyrazolyl)methanesulfonate were obtained by treatment of Re2O7 or [ReOCl3(PPh3)2], respectively, with Li[SO3C(pz)3], whereas [ReCl3{HC(pz)3}] (3), [ReCl3{HC(3,5-Me2pz)3}] (4) and [ReCl4{η2-HC(pz)3}] (5) were prepared by reaction of [ReOCl3(PPh3)2] (3,4) or [ReCl4(NCMe)2] (5) with hydrotris(pyrazolyl)methane HC(pz)3 (3,5) or hydrotris(3,5-dimethyl-1-pyrazolyl)methane HC(3,5-Me2pz)3 (4). [ReO{SO3C(pz)3}{OC(CH3)2pz}][ReO4] 6, with a chelated pyrazolyl-alkoxide, was derived from an unprecedented ketone-pyrazolyl coupling on reaction of crude 1 with acetone. The compounds have been characterized by elemental analyses, IR and NMR spectroscopies, FAB-MS spectrometry and cyclic voltammetry and, in the case of 5 and 6, also by single-crystal X-ray diffraction. The electrochemical EL Lever parameter has been estimated, for the first time, for the SO3C(pz)3− and oxo ligands allowing the measurement of their electron-donor character and comparison with other ligands. Compounds 1, 2 and 6 appear to be the first tris(pyrazolyl)methanesulfonate complexes of rhenium to be reported.

2006-09-06Journal article

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